1. (Field of the Invention)
The present invention relates to a method of producing a spirofluorenol compound useful as a starting material for producing a photochromic compound.
2. (Description of the Related Art)
Recently, the chromene derivatives, especially spiroindenonaphthopyranes draw much attention as photochromic compounds for their fast color developing-fading rates, easy color tone controllability and high color fastness. In these spiroindenonaphthopyranes, spiroketal type compounds (International Patent Publication No. 10-508031), biphenyl type spiro-compounds and phenanthrene type spiro-compounds (Japanese Unexamined Patent Publication (Kokai) No. 2000-34418 and No. 2001-192378) are known. In particular, the latter two compounds feature high color-developing sensitivity, fast fading rate and excellent color fastness.
It has been known that these compounds are obtained by modifying the properly substituted indenonaphthopyrane-one, prepared by several steps, represented by the following formula (5) (Japanese Unexamined Patent Publication (Kokai) No. 2000-34418 and No. 2001-192378). However, according to the above method, a strict purification must be needed to obtain desired developing color tone because a trace of impurity may exhibits photochromic properties and may developing undesired color tone when using the indenonaphthopyrane-one, it exhibits photochromic properties by itself, as the intermediate.

On the other hand, it has been known another method, which is little likely to form photochromic impurities, for producing desired chromene derivatives from spirofluorenol (Japanese Unexamined Patent Publication (Kokai) No. 2001-192378).
According to the above method, a hydroxyfluorenone having a phenolic hydroxyl group is reacted with a Grignard reagent, and then reacted under acidic condition to form spirofluorenol. As a result, excess amounts of Grignard reagent is required to complete the former reaction.